Resistive stability of 2∕1 modes near 1∕1 resonance

Brennan, D. P.; Turnbull, A. D.; Chu, M. S.; Haye, R.J. La; Lao, L. L.; Osborne, T. H.; Галкин, С. А.

doi:10.1063/1.2515224

Cited by 20 publications

(29 citation statements)

References 20 publications

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“…A significant stable region above the experimental trajectory exists where, during the flattop phase of the discharge, the motion of the trajectory is isolated near q min ∼ 1.1 and β N ∼ 2.6. Previous studies of the stability of the 2/1 mode in low q min DIII-D equilibria have shown similar results [12] for a similar discharge. The conclusion of the previous study in [12] was that the minimum q value of the experimental trajectory entered the resistive unstable zone long enough for onset at the time when the mode was observed.…”

Section: Mhd Stability Analysissupporting

confidence: 76%

“…Previous studies of the stability of the 2/1 mode in low q min DIII-D equilibria have shown similar results [12] for a similar discharge. The conclusion of the previous study in [12] was that the minimum q value of the experimental trajectory entered the resistive unstable zone long enough for onset at the time when the mode was observed. Increasing β N , even small amounts ∼0.2, in such discharges leads to the onset of a n = 1 resistive instability [16].…”

Section: Mhd Stability Analysissupporting

confidence: 76%

“…This proximity to q = 1 causes a non-resonant but significant 1/1 and 2/2 response around the magnetic axis, which plays a critical role in the physics of the equilibrium state and is sensitive to small changes in q min . In particular, it has been shown to affect the ideal and resistive MHD stability [12].…”

Section: Equilibriummentioning

confidence: 99%

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Energetic particle effects on n = 1 resistive MHD instabilities in a DIII-D hybrid discharge

2012

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The δf kinetic-magnetohydrodynamic (MHD) model in the 3D extended-MHD code NIMROD is used to perform a linear simulation study of energetic particle effects on the n = 1 mode in a DIII-D hybrid discharge. The hybrid discharge has a long steady state with low q min ≳ 1 at high confinement, is useful for numerous physics studies, and is a candidate operational scenario for burning plasma experiments. But hybrid discharges are limited to moderate βN by the m/n = 2/1 instability, which onsets with small increases in βN. Using realistic equilibria based on experimental reconstructions from DIII-D, the stability of the n = 1 mode during the steady state of a hybrid discharge is computed over a (q min, βN) space. MHD stability analyses do not indicate instability to the n = 1 for small increases in βN above that of the experimental discharge. Our results show that energetic particles significantly change the stability map in (q min, βN) parameter space from the MHD-only result. Unstable modes are driven by energetic particles far into the MHD stable region in (q min, βN) space. Three different unstable regions are identified, each being defined by the fastest growing mode and distinctly different frequencies. We examine sample eigenmodes from these three regions. At low q min ∼ 1 the drive is associated with the fishbone mode, while the higher q min ≳ 1.12 the drive is associated with the Beta induced Alfven eigenmode. Overlaying the experimental trajectory in the same (q min, βN) parameter space shows that all three regions are in proximity to the trajectory. In the higher q min region a mode with a broad m/n = 2/1 dominant structure is most unstable, while in the region of the trajectory the most unstable mode has a m/n = 1/1 component localized near the axis. Experimentally, a nonlinearly saturated m/n = 1/1 structure is observed localized near the magnetic axis. This agreement suggests that the m/n = 2/1 mode may be triggered by energetic particles in these discharges.

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Section: Mhd Stability Analysissupporting

confidence: 76%

Section: Mhd Stability Analysissupporting

confidence: 76%

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Energetic particle effects on n = 1 resistive MHD instabilities in a DIII-D hybrid discharge

2012

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“…The relatively fast impulse at an ELM and the relatively long s R in the MRE, suggests an ideal coupling of the NTM to the ELM, which is a peeling/ballooning mode; this could result in a transient negative "pole" in the D 0 term. 35 The evolution of the island width w is taken as…”

Section: B Resistive Recovery Of the Island Widthmentioning

confidence: 99%

Hybrid-like 2/1 flux-pumping and magnetic island evolution due to edge localized mode-neoclassical tearing mode coupling in DIII-D

et al. 2012

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Direct analysis of internal magnetic field pitch angles measured using the motional Stark effect diagnostic shows m=n ¼ 2=1 neoclassical tearing modes exhibit stronger poloidal magnetic flux-pumping than typical hybrids containing m=n ¼ 3=2 modes. This flux-pumping causes the avoidance of sawteeth, and is present during partial electron cyclotron current drive suppression of the tearing mode. This finding could lead to hybrid discharges with higher normalized fusion performance at lower q 95 . The degree of edge localized mode-neoclassical tearing mode (ELM-NTM) coupling and the strength of flux-pumping increase with beta and the proximity of the modes to the ELMing pedestal. Flux-pumping appears independent of magnetic island width. Individual ELM-NTM coupling events show a rapid timescale drop in the island width followed by a resistive recovery that is successfully modeled using the modified Rutherford equation. The fast transient drop in island width increases with ELM size.

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“…This result is actually not uncommon, as the coupling of m/n neoclassical tearing modes to m--1/n core kinks has been documented in TFTR [109] and ASDEX -Upgrade [110] and predicted by theory [111]. Indeed, the destabilization of the 2/1 mode without an obvious trigger in Ref.…”

Section: Section 42: Continuous Coupled N=1 Modesmentioning

confidence: 94%

Calculation of the non-inductive current profile in high-performance NSTX plasmas

et al. 2011

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The constituents of the current profile have been computed for a wide range of high-performance plasmas in NSTX (Ono et al 2000 Nucl. Fusion 40 557); these include cases designed to maximize the non-inductive fraction, pulse length, toroidal-β or stored energy. In the absence of low-frequency MHD activity, good agreement is found between the reconstructed current profile and that predicted by summing the independently calculated inductive, pressure-driven and neutral beam currents, without the need to invoke any anomalous beam ion diffusion. Exceptions occur, for instance, when there are toroidal Alfvén eigenmode avalanches or coupled m/n = 1/1 + 2/1 kink-tearing modes. In these cases, the addition of a spatially and temporally dependent fast-ion diffusivity can reduce the core beam current drive, restoring agreement between the reconstructed profile and the summed constituents, as well as bringing better agreement between the simulated and measured neutron emission rate. An upper bound on the fast-ion diffusivity of ∼0.5–1 m2 s−1 is found in ‘MHD-free’ discharges, based on the neutron emission, the time rate of change in the neutron signal when a neutral beam is stepped and reconstructed on-axis current density.

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Resistive stability of 2∕1 modes near 1∕1 resonance

Cited by 20 publications

References 20 publications

Energetic particle effects on n = 1 resistive MHD instabilities in a DIII-D hybrid discharge

Energetic particle effects on n = 1 resistive MHD instabilities in a DIII-D hybrid discharge

Hybrid-like 2/1 flux-pumping and magnetic island evolution due to edge localized mode-neoclassical tearing mode coupling in DIII-D

Calculation of the non-inductive current profile in high-performance NSTX plasmas

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